Optical coherence tomography (OCT) is a light-optical imaging method used in the medical field for, among the things, recording images inside a vessel. For this purpose there is provided an OCT catheter with an OCT imaging device which has at least one light guide via which light to be emitted by the OCT imaging device is supplied and light reflected by the vessel wall or the like and recorded by the OCT imaging device is guided to an image processing device disposed extracorporeally. An OCT catheter of this kind is usually incorporated in a guide catheter in which it is displaceable. The two catheters together constitute a catheter device.
In its application in the vascular system, optical coherence tomography is constrained by the fact that transmitted light, typically light in the near infrared region with a wavelength of e.g. 1300 nm, is scattered by blood constituents. Compared to scattering, absorption phenomena at the typical OCT wavelengths are minimal, i.e. scattering effects constitute the primary quality-influencing factor. These scattering effects mean that, during intravascular OCT imaging, the blood must be removed in a suitable manner from the vascular region under examination in order to image the vessel wall. When using a catheter device of the above-mentioned type, this is done by occluding the vessel and therefore the blood flow via a reversibly inflatable balloon disposed on the guide catheter, the occlusion being located preferably proximally to, i.e. upstream of, the imaging location so that only a small amount of liquid or gas for flushing out the residual blood still present in the vessel needs to be introduced distally, i.e. downstream. In this way, once any further inflow is prevented as a result of the occlusion, the vessel can be kept cell-free and good image quality achieved.
However, the problem is that, because of the occlusion of the vessel and therefore of the blood flow, the pressure in the occluded vascular region falls to venous values. This means that, in the case of a normal arterial pressure of approximately 100 mmHg, a pressure of approximately 20 to 30 mmHg obtains in the occluded vascular area. Because of the low-pressure, the anatomy of the vessel, which is expandable like an elastic tube, changes, i.e. the vessel that was dilated at normal arterial pressure contracts as a result of the pressure loss. The OCT images obtained therefore reflect a situation not occurring in natura, i.e. during natural blood flow through the vessel. Also, because of the contracting of the vessel, possible pathologies are sometimes not visible, as they may disappear in vascular folds.